Opacifier for vitreous enamels



May 7, 1940.

w. J. HARsHAw Ax. 2.200.170

OPACIFIER FOR VITREOUS ENAMELS "Sheets-Sheet 1 original Filed sept. 15,1938 3 a'lo Rzc once.

IGMTCQ-Sbm-v ATTORNEY.

May 7, 1940. w. J. HARsHAw ET Al.v 2,200,170

OPACIFIER FOR VITREOUS ENAMELS Original Filed Sept. l5, 1938 3Sheets-Sheet 2 Znc.

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lNvENTOR.

ATTORNEY,

May 7, 1940- w. J. HARsHAw Er AL 2,200.170

QPACIFIER FOR VITREOUS ENAMELS Original Filed Sept. 15, '1938 3lShemts-Shee'. 3

BY MM ff/6mm ATTORNEY.

Patented May 7, 1940 OPACIFIER FOR VITREOUS ENAMELS William J. Harshaw,Shaker Heights, and William D. Stiliwell, South Euclid, Ohio, assignorsto The llarshaw Chemical Company, Ohio, a corporation ot Ohio Elyria,

original application september 15, 193s, serial Divided and thisapplication November 1, 1939, Serial No. 302,416

9 Claims.

'I'his invention relates to mill addition opaciiiers for vitreousenamels.

Opaciilcation of vitreous enamels is accomplished either by smelteradditions in the production of an enamel frit or by mill additions tothe quenched frit in the production of the enamel slip. Smelter additionopaciflers are often not suitable for mill addition opacification andvice versa.

In our prior United States Patent, No. 2,033,707, we have describedpre-calcined mill addition opaciiiers capable of imparting to vitreousenamels a high degree of opaciilcation. In enamels wherein we have usedopacifiers according to our said patent, we have experienced, especiallyin the case of titanium containing compositions and to some extent alsoin zirconium containing compositions, a deficiency of reflectance in theviolet.

In the case of titanium compositions this deciency appeared as adistinctly perceptible yellowish coloration in the enamel. Accordingly,it is highly desirable to overcome the indicated tendency to yellowcoloration in the enamel by increasing its power of reflectance ofviolet light.

In accordance with the present invention it now becomes possible toovercome the undesirable tendency to yellow coloration and produceopaciflers similar to those of our said patent but productive oi enamelsexhibiting desirable high reilectance in the violet end of the visiblespectrum.

In the drawings, Fig. 1 is a graphic representation of the effect oi'calcining varying quantities of iluorine material with constantquantities of the other ingredients, in a mill addition opacifieraccording to the invention, on the opacity and color of a porcelainenamel opaciiled therewith; Fig. 2 is a graphic representation of theeffect of time and temperature of calcination on mill additions,according to the invention, as measured by the opacity of the enamelopaciiied therewith; Fig. 3 is a graphic representation oi thecomparative eilects of varying amounts of tin oxide and a typical milladdition according to the present invention, on two conventional enamelfrits of diverse types as measured by the opacity of the resultingenamel; and, Figs. 4 to 9 inclusive are substantial copies of recordingspectrophotometer charts showing the effect of various oi the novel (Cl.10G-36.2)

oxide to Sb205) oxide of titanium (T102) or oxide of zirconium (ZrOz) orsuitable materials capable of yielding one or more of the same; a basicoxide (such as CaO, BaO, SrO, MgO, A1203, ZnO, or partial substitutionsof alkali metal oxides there- 5 for), or suitable materials capable ofyielding the same; and a suitable fluorine containing material (such asCaFz, suitably in the form of fiuorspar, BaF2,fNaF, MgFz, NzZIFe, CaZIF,NaaAlFs, and

vmaterials capable on calcination of producing l( same, such as MgSlFs,HzSiFe plus CaO, MgO plus HF, etc. when used as mill addition opacifiersare capable of producing excellent opaciflcation and with no tendency toyellow coloration of the enamel. If, however, the iluorine material isl5 omitted, a distinct deficiency in reflectance of violet light can bedemonstrated, which is, slight in the zirconium compositions and more orless pronounced in the case of the titanium compo sitions.

We believe that complex reactions occur during the calcination but donot completely understand the nature of such reactions. Accordingly, thecalcination products of the ingredients used in the production of thenovel opacifier compositions are treated as containing" certainconstituent oxides and iiuorine material, or as having a certaincomposition without thereby 1ntending to limit the invention to anyparticular state of combination, solution or admixture of such oxidesand iluorine material.

We have discovered that upon employment of increasing quantities of thefluorine containing materials, an increasing improvement is noted in thereflectance of violet light up to a point that the objectionable yellowcoloration is no longer perceptible. This bleaching or whitening effectis accompanied by a decrease in opacity (total reflectance of whitelight) up to about the point where the yellow color is n'o longerperceptible. Surprisingly, however, still further additions of theiluorine containing-materials, gradually increase the opacity of theresulting enamel to a value higher than when no iluorine material waspresent. Addition of the iluorine containing material as a smelteraddition Ain the production of the frit does not produce the desiredeiiect. The essential distinction between smelter additions` and milladditions, is, as is well known, one of heating time, and, where theterm mill addition or words of like import are used herein, it isintended to cover equivalent procedures where long heating of theopacifier with the. frit is avoided. calcination of the ingredients ofthe mill addition opaciflers of the present invention, other 5E than theiluorlne containing material. followed by incorporation ci theseparately calcined or uncalcined ilumine-containing material bygrinding, produces a mill addition productive of enamels having theobjectionable yellow coloration to the same extent as if no fluorinecontaining material had been addedbut with slightlyv lower opacity.Calcination of calcium antirnonate with iluorspar or synthetic CaFa,produces a mill addition productive of enamels of lower opacity than iiopacified with calcium antimonate alone. Enamels opacied with calciumtitanates are white or slightly creamy in color. The addition o1fluorspar makes them distinctly yellow and without improving theiralready poor opacity. We are aware that uorides are commonly used assmelter additions, but, as stated, they are not effective for ourpurpose when so used.

We are able to obtain an enamel of very excellent opacity, but decientin reflectance of violet light, by using as a mill addition opacier acalcinatlon product of the following composition:

Parts by weight CaO 20 SbzOa 46 T102 34 If to the batch oi which theabove composition is the calclnation product is added 10 parts by weightof a suitable uorine material, e. g., uorspar, and the resultingcalcination product is employed as a mill addition opacifler, an enamelis produced which is free from the objectionable yellow coloration.

The sample composition given above is typical but may be variedconsiderably without departingfrom the scope of the invention. We preferto operate, and obtain best results by operating,

within the following range of composition.

` Parts by weight CaO 18 to 22 SbaOs 44 to 46 T102 32 to 34 CaFa 5to 30vparts TiOa were used, the CaFi content being varied from 3.5 to 14. Thevertical line A indicates approximately the point at which the yellowcoloration disappeared. At 5 per cent the coloration is very slight.

Our experiments indicate that the uorine material should have a particlesize of from 100 mesh to 200 mesh for best results although the degreeof subdivision is not critical.

As above indicated, the oxides need not be employed as such but mayl beformed from other materials on calcination. Some sample batchcompositions are as follows: i

Parts by weight CaCOa (precipitated chalk) 64.5 SbeOs 75.0 T102 62.0HNOa (conc.) v 32.0 CaFz (uorspar) 38.0

CaCO; (precipitated chalk) 64.5 SbaOa 75.0

Parts by` e weight 1101-...' 62.0 HNO: (conc.) 32.0 CaFz (fiuorspar)44.0

CaCOa 64.5 CaFa. 20.0 Shao; 75.0 T102 62.0 HNOa (conc).y 32.0

CaCO; 40.6 CaF2 34.6 SbgOa 68.6 T102 56.6 H20 24.0 C8. (NO3) a' H2O 33.4

ZnO 44.8 T102 66.2 SbzOa 80.0 NaF1 40.0 HNOa. (conc.) 28.0

BaCOa 394 T10: 240.3 SbzOa 291.5 CaFz 105.0 HN03 (conc.) 150.0

NaNOa 42.5 CaCOa 150.0 Ti02 240.0 Sb203 291.0 NaF 80.0 HNOa (conc.)115.0

CaCOa 100.0 MgCOa 168.6 T102 240.3 SbzOs 291.5 MgSiFa 80.0 HNO: (conc.)80.0

MgCOs 253.0 T102 240.0 SbaOa 291.5 MgSiFe 80.0 HNOa (conc.) 80.0

CaC03 59.2 Sb203 y 86.3 ZiOz `'71.0 NazZrFa 30.0 HN03 (conc.) y40.0

Calcination is carried out at a temperature preferably from 1000u C. to1150o C., actual batchv temperature, and preferably in an oxidizing kilnatmosphere. The time required varies according to the temperature andother conditions, especially the size of the batch, larger batchesrequiring longer time. As is clear from Fig. 2, the reilectance isnearly fully developed by three hours ring at 1150a C. whereas five orsix hours are required at l000 C. While other temperatures may be usedsuccessfully, as indicated in Fig. 2, we prefer five hours or longer at1000,C. to 1100 C.

The above described .mill-addition-opacifying compositions are suitablefor use in enamel frits generally for production of white enamels. -InFig. 3 we have compared'our novel mill addition with tin oxide in a lowreectance enamel (curves I5 and I6), and in a super opaque yenamel(curves I1 and I8), using the calcination product of the batch formulafirst-above given. The samples corresponding to the lines I5 and I1 areopacied with tin oxide in the quantities shown,

' and I8 were opacied with a calcium-antimonytitanium-uorine compositionaccording to the invention, as indicated.

The following examples will be illustrative of the ect of typicalexamples of our novel mill additions on theresulting enamels in respectto reectance of violet light:

Example I Composition ofmill addition: l

CaO parts by weigh 16.6 sbzos.- do .47.7 T102 d0 35.5

Amount of. mill addition agent added to enamel frit per cent-- 6 Thereilectance of violet light inthis case is l shown clearly in Fig. 4,wherein reflectance in per cent (MgCOa=l00%) is plotted against wavelength of light. This view is a substantial copy of a test sheet made ona recording spectrophotometer.

above composition; the line 2 (full) was produced by an enamel opacifledwith a composition similar except being calcined with 10 parts by weightuorspar. l

The reilectance of this sample is shown in Fig. 5, the line 3 (broken)being a record of a test on an enamel containing the above opacifler.The line 4 (full) is a record of a test of an enamel opacied with acomposition similar to that above except being calcined with 20 parts byweight of sodium fluoride.

Example III Composition of mill addition:

CaO parts by weight-- 7.8 A1203 do 14.2 SbaOs do 44.6 T102 do .33.4

. Amount of mill addition agent added to enamel frit per cent-- 6 Thereilectance of this sample is shown in Fig. 6, the line 6 (broken) beinga record of a test on an enamel containing the above opacliier.v

The line 6 (full) shows the result of a test of an enamel opacied with acomposition similar to the above except being calcined with l13% offluorspar. The line 'I (dot and dash) shows the result of a test on anenamel opacifled with av composition like that above except for the substitution of cryolite for a part (25%) of the iluorspar.

In Fig. 7 we have shown by the line 8 (broken) the reflectance of aporcelain enamel opacitled with the above composition and in line 9(full) the same but opacied with a composition varied In this View, theline I (broken) was produced by an enamel opaciiied with the containingapproximately:

in'that'with the above composition ".vas calcined ,11.3%'of NaF.-

Example V Composition of mill addition:

' CaO parts byiweight '14.0 SbzOs L d0 40.0 ZrOz do 46.0

Amount of mill raddition agent added to enamel frit per cent-- 6 In Fig.8 we have shown the results of reflectance tests in porcelain enamel ofthe above opacier composition (line I Il, broken) and a compositionsimilar except for the calcination therewith of In Fig. 9 we have shownthe results of opacii'lcation with the above composition (line I2,broken), with the same as varied by calcining therewith 20 parts byweight of fluorspar (line I3, dot vand dash), and also as varied bygrinding with the calcined composition 20 partsby weight of previouslycalcined fluor'spar (line I4, full). It will be noted that when thefiuorine material is calcined with the other constituents of the milladdition', the desired eiect is produced.

This application is a division of our co-pending application, Serial No.230,104, led September 15, 1938, which was a continuation-impart of ourapplication, Serial No. 178,760, filed December 8, 1937.

Having thus described claim is:

l. In making a vitreous enamel, ilring together an oxide of antimony,available uorine material, an oxide from the group consistingl oftitanium and zirconium, an oxide of a base forming metal and anoxidizing agent, mixing the product in a mill `charge withenamel iritand grinding.A

2. A mill addition opacier for vitreousenamels, the same beinga'calcination product, and containing: an oxide of a base forming metal,SbzOa, TiOz and a iiuoride.

3. A mill addition opacier for vitreous enamels, the same being acalcination product containing an oxide of a base forming element,SbaOs, T102, and a iluoride capable of preventing preceptible yellowcoloration of resulting enamels, said uoride being used in quantity morethan suflicient to prevent such coloration.

4. A mill addition opacifler for vitreous enamels, the same containing:ZnO, Sb205, T102, and a iiuoride.

5. A mill addition opaciiier for vitreous enam' els, the same being acalcination product and our invention, what we Parts by weight ZI10 22Sb205 45 T102 33 and a fluoride from 5% to 30% of the weight of saidoxides.

6. A mill addition opacifler for vitreous enamels, the same containing:BaO, SbzOs, TiOz, and a. uoride.

7. A mill addition opacier for vitreous enamels, the same being acalcination product and containing approximately:

and CaFz 5% to 30% of the combined weight of said oxides.

8. A mill addition opaciier for vitreous enamels, the same containing:MgO, SbzOs, TiOz, and a uoride.

9. A mill addition opnancierl for vitreous enamels, the same being a.calcinationl product and containing approximately:

Parts by weight MgO 16.2

SbzOs 48.2 TiOz 35.6

